Interactions in an Ecosystem, Biology tutorial


Interactions between living organisms are as well termed to as associations. Living organisms encompass a broad range of interactions and such interactions might take place between individuals from populations of similar species or different species. These interactions might be competition for food, mates or parasitism.

Interactions in an Ecosystem:

1) Competition:

Competition occurs when individuals struggle for a common resource that might be in short supply. Illustration: Competition for food, mates, light and so on. The phenomenon of competition was studied by Guaze. He employed various species of paramecia. He proposed a law known as the law of competitive exclusion. In conclusion, the law describes that when two species are directly competing for a common resources that is in short supply, the species which is better adapted for utilizing the resource will survive whereas the other species goes extinct locally. However if their needs are slightly different, both of them might co-exist. There are mainly two types of competition:

a) Intra-specific competition which takes place among individuals of similar species example:  Paramecium aurelia and Paramecium caudalum.

b) Inter-specific competition which takes place among individuals of distinct species. For instance: competition for nutrients among rice plants and weeds.

2) Predation:

This is a kind of interaction in which the predator, generally a carnivorous animal kills and feeds on the other, termed to as the prey. For illustration: lion feeding on antelope, cat on mouse and so on the predator is, in most situations, stronger and bigger than the prey.

3) Parasitism:

An organism which lives in or on other organism (that is, host) and based on it for food and shelter is termed as a parasite. The parasite advantages, though the host is harmed however is not generally killed. Parasitism is an inter-specific interaction. The relationship is accountable for many animal and plant diseases as it weakens the system of host and makes it less productive. There are different kinds of parasites as follows:

a) Ectoparasites are those which live on the body of the host example: aphids on citrus plants, mistletoe plants on the trees wish for water and minerals salts, lice bugs and fleas live on the skin of animals.

b) Endoparasites are the parasites which inhabit internal organ and tissues of animals and plants example: Ematodes in tomato roots, blood parasites like plasmodium and a few trematodes; Ascaris, tapeworms and hookworms live in the intestines of animals.

c) Facultative parasites are the organisms which can live as parasites and also being free.

d) Obligate parasites are such that can survive only on/in a host. They can't live freely example: plasmodium. The Parasites which cause diseases are termed as pathogens.

4) Symbiosis:

In present times, the word symbiosis is employed to explain any close relation among two species. If both species take advantage from the relation then it is stated to be mutualism. This leads to a condition where the survival of each is based on the other.

a) Root nodules: In this, the legume plants like cowpea play host to rhizobium, a bacteria, that is, the symbiont. The host here gives carbohydrates and protection to the bacteria, which in turn fixes nitrogen from the air and transforms it into amino acids. The host employs the amino acid.

b) Mycorhiza:  This symbiotic interactive exists among fungi, the symbiont and certain roots of plants example: Pine growing in the acid soils. An enzyme that the fungi employs to digest leaf litter is given by the Pine (that is, the host) whereas the fungi gives mineral ions to the Pine.

c) Lichens:  Lichens are the symbiotic relation build up of fungi and algae, the algae lives in the fungus mycelium. Whereas the fungi (host) provide shelter and mineral ions to the algae, the algae give oxygen and photosynthetic products to the fungi.

5) Commensalism:

This interaction profits only one of the interactants, that is, the commensal. The other partner is not harmed or affected in any manner. Illustrations are:

a) Epiphytes in the forest grow on branches of trees to be close to light whereas roots tap water from the soil in the crevices of tree barks. The tree gives support.

b) The remora fish join itself to the shark and is transported all over the place and eats food crumbs from leftover of the shark's meal however is not harmed by the shark, though the shark doesn't gain from this association.

c) Fiat worms on the gills of crabs feed on left-over scraps from the crab's meal whereas they don't hurt the gills of crab.

d) The cattle egret (that is, white heron) in its association with cattle feeds on insects from the grass being fed on through the cattle however the cattle neither gain nor lose from the relationship. Necessary commensals stay with a single species.

6) Saprophytism:

These are the organisms which get their food from dead organic matter, like dead plants and animals. Their feeding action causes decay of organic matter. Saprophytes are fungi bacteria (like mucor and mushroom) and moulds.

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